Making A Microwave Sandwich from Tunable Impedance Sheets for Complex Permittivity Extraction

This study presents a method for extracting the complex permittivity of an unknown material positioned between two tunable impedance sheets. By illuminating this configuration with a transceiver antenna and monitoring the changes in the resonant profile of the reflected signal over the tunable space, the complex permittivity of the unknown material can be determined. This method was investigated using pairs of inductive and capacitive impedance sheets that were used to sandwich dielectric materials with permittivities up to 10 and loss tangents up to 0.4. Here we show that inductive sandwiching sheets provide higher sensitivity with respect to loss tangent than capacitive sandwiching sheets; however, the range of detectable values is more limited. This method requires only scalar reflection measurements and therefore provides a low-cost method of wireless complex permittivity extraction.